As a method for drilling a copper-clad laminate or a multi-layer board used for a printed wiring board material, a method in which a simple aluminum foil or an entry sheet for drilling obtained by forming a resin composition layer on a surface of an aluminum foil is disposed as an auxiliary sheet on the top surface of a copper-clad laminate, a multi-layer board or a stack of two or more copper-clad laminates or two or more multi-layer boards before drilling, is generally adopted. In recent years, high-quality drilling is required with regard to a printed wiring board material in accordance with a demand of improvement in reliability and a progress of high-densification. For example, an improvement in hole registration accuracy or a decrease in hole wall roughness is required. For coping with the requirement of high-quality drilling, a hole-making method which utilizes a sheet of a water-soluble resin composition such as polyethylene glycol (for example, JP-A-4-92494), a lubricant sheet for making a hole obtained by forming a water-soluble resin composition layer on a metal foil (for example, JP-A-6-344297) and an entry sheet for making a hole obtained by forming a thermosetting resin composition thin film on an aluminum foil and further forming a water-soluble resin composition layer (for example, JP-A-2003-136485) have been proposed and practically adopted. Here, the thickness of a water-soluble resin composition layer formed on a metal foil is very important for improving the quality of hole wall.
In a conventional laminating process, it is possible to laminate a water-soluble resin composition layer having a thickness of at least 50 μm to a metal foil surface. However, a solution method has the following problems. When a low viscosity solution of a water-soluble resin composition is thickly applied to a metal foil surface by a coating process, the solution drips during the application and drying and foaming occurs during the drying and the solidification of the water-soluble resin composition. Therefore, production is difficult by the solution method. When a thick water-soluble resin composition layer is formed by applying a water-soluble resin composition solution thickly and drying and solidifying the applied water-soluble resin composition through a method in which a clearance between an applied coating portion and a metal foil is broadened at an application time or through a method in which two water-soluble resin composition layers are successively formed from two applied coating portions respectively, air bubbles exist in the water-soluble resin composition layer and in addition the smoothness of the surface of the water-soluble resin composition layer decreases. The presence of air bubbles in the water-soluble resin composition layer and the decrease in the smoothness of the water-soluble resin composition layer surface adversely affect hole registration accuracy at a drilling time.